This invention relates generally to alignment instruments used in construction and, in particular, to an apparatus for aligning individual sections of pipe in a pipeline. More particularly the invention relates to a self-aligning laser beam method and apparatus for laying pipe such as sewer pipe.
It has long been known to utilize a beam of collimated light, directed in the desired direction, for laying a pipeline in order to align individual sections of pipe in a straight line and at a particular grade. A target is positioned at the end of the pipe being positioned and is utilized to manipulate new sections of pipe until the light beam is centered on the target. After the section of pipe is secured, the target is moved to the next section of pipe to be added. Such technique is disclosed in U.S. Pat. Nos. 3,488,854; 3,591,926; and 3,634,941, all assigned to the assignee of the present application.
One difficulty with such technique is that the apparatus must be disassembled and stowed away at the end of each workday. If less than the entire pipeline is laid in a day, it is necessary to set up the equipment the next day in order to resume construction. In order for the user to extend a previously laid portion of pipeline, two workers were required; one to set up and monitor the target and the other to set up and align the laser unit until the laser beam strikes the center of the target as observed by the other worker. This process is inefficient because it requires two workers who must communicate and coordinate their actions at a considerable distance either via radio or, if none is immediately available, via shouts and hand signals.
In order to overcome such difficulties, it has been proposed to provide an active target which is equipped with a plurality of photocells arranged in a particular pattern to automatically align the laser beam. The active target includes a controller which responds to a laser beam striking the photocells in order to transmit a control signal to a controller in the laser. The laser responds to the control signal by repositioning the beam. While such device eliminates the requirement for two workers, it introduces additional cost and complexity in the apparatus. The active target requires electronic circuitry and must be powered from a separate battery.